The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a functional block diagram of an engine system 100 is presented. Air is drawn into an engine 102 through an intake manifold 104. The volume of air drawn into the engine 102 is varied by a throttle valve 106. The air mixes with fuel from one or more fuel injectors 108 to form an air/fuel mixture. The air/fuel mixture is combusted within one or more cylinders 110 of the engine 102 to generate torque. An engine control module (ECM) 112 modulates torque output by the engine 102 via, for example, the fuel injector 108 and/or the throttle valve 106.
Exhaust resulting from the combustion of the air/fuel mixture is expelled from the cylinders to an exhaust system. The exhaust may include particulate matter (PM) and gas. More specifically, the exhaust gas may include nitrogen oxides (NOx), such as nitrogen oxide (NO) and nitrogen dioxide (NO2). The exhaust system includes a treatment system 114 that, among other things, reduces the respective amounts of NOx and PM in the exhaust.
The treatment system 114 includes a diesel oxidation catalyst (DOC) 116, a dosing agent injector 118, and a catalyst 120. The DOC 116 removes, for example, hydrocarbons and/or carbon oxides from the exhaust. The dosing agent injector 118 injects a dosing agent into the exhaust stream, upstream of the catalyst 120. The catalyst 120, more specifically, is a selective catalytic reduction (SCR) catalyst. The dosing agent reacts with NOx in the exhaust passing the SCR catalyst 120 resulting in nitrogen (N2) and water (H2O).
The ECM 112 includes a dosing module 130 that controls the mass flow rate of dosing agent injected (DAIN) via the dosing agent injector 118. The dosing module 130 adjusts DAIN based upon signals from one or more NOx sensors 138 and 140 and/or signals from one or more temperature sensors 134 and 136. Additionally, the dosing module 130 may adjust DAIN based upon signals from other sensors 142. For example only, the other sensors 142 may include a manifold absolute pressure (MAP) sensor, a mass air flow (MAF) sensor, a throttle position sensor (TPS), an intake air temperature (IAT) sensor, and/or any other suitable sensor.
To perform a NOx reduction, the SCR catalyst 120 stores NH3 provided by the dosing agent. The mass of NH3 stored by the SCR catalyst 120 is referred to as current storage. The percentage (e.g., 0-100%) of NOx that is removed from the exhaust is referred to as conversion efficiency and is dependent upon current storage. For example only, as current storage increases, conversion efficiency also increases.
To maintain a predetermined conversion efficiency, the dosing module 130 adjusts DAIN to provide a corresponding current storage. However, the SCR catalyst 120 may be capable of storing up to a maximum mass of NH3, which is referred to as maximum storage capacity. Conversion efficiency may be maximized when the current storage of the SCR catalyst 120 is at maximum storage capacity. Accordingly, the dosing module 130 adjusts DAIN to maintain current storage at or near the maximum storage capacity to maximize conversion efficiency.